Infection is the major cause of morbidity and mortality in patients with malignant disease. We are developing and evaluating the utility of various techniques and procedures to reduce the incidence of severe infection in cancer patients. The role of oral absorbable antibiotic prophylaxis is being evaluated in patients receiving standard doses of chemotherapy, and the role of protected environments (laminar air-flow room isolators) is being studied in patients receiving intensive chemotherapy. We are also evaluating new methods for detecting occult infections in neutropenic patients, e.g., gallium scanning in conjunction with white cell transfusion and the ELISA inhibition assay for fungal antigen. Empiric and specific antibiotic treatment of granulocytopenic patients with fever of unknown origin or proven infections is being prospectively studied, and the role of newer antimicrobial agents is also being investigated. The role of chemically defined immunoregulatory agents is being evaluated in in vitro and in vivo models to develop methods of improving host defenses following immunosuppressive chemotherapy and reduce the incidence and severity of infectious complications.